jffs2: reduce stack usage in jffs2_build_xattr_subsystem()

Use kcalloc() for allocation/flush of 128 pointers table to
reduce stack usage.

Function now returns -ENOMEM or 0 on success.

stackusage
Before:
./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     1208
dynamic,bounded

After:
./fs/jffs2/xattr.c:775  jffs2_build_xattr_subsystem     192
dynamic,bounded

Also update definition when CONFIG_JFFS2_FS_XATTR is not enabled

Tested with an MTD mount point and some user set/getfattr.

Many current target on OpenWRT also suffer from a compilation warning
(that become an error with CONFIG_WERROR) with the following output:

fs/jffs2/xattr.c: In function 'jffs2_build_xattr_subsystem':
fs/jffs2/xattr.c:887:1: error: the frame size of 1088 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
  887 | }
      | ^

Using dynamic allocation fix this compilation warning.

Fixes: c9f700f8 ("[JFFS2][XATTR] using 'delete marker' for xdatum/xref deletion")
Reported-by: Tim Gardner <tim.gardner@canonical.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Ron Economos <re@w6rz.net>
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Cc: stable@vger.kernel.org
Message-Id: <20230506045612.16616-1-ansuelsmth@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/jffs2/build.c

@@ -211,7 +211,10 @@ static int jffs2_build_filesystem(struct jffs2_sb_info *c)
 		ic->scan_dents = NULL;
 		cond_resched();
 	}
-	jffs2_build_xattr_subsystem(c);
+	ret = jffs2_build_xattr_subsystem(c);
+	if (ret)
+		goto exit;
+
 	c->flags &= ~JFFS2_SB_FLAG_BUILDING;
 
 	dbg_fsbuild("FS build complete\n");

fs/jffs2/xattr.c

@@ -772,10 +772,10 @@ void jffs2_clear_xattr_subsystem(struct jffs2_sb_info *c)
 }
 
 #define XREF_TMPHASH_SIZE	(128)
-void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
+int jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
 {
 	struct jffs2_xattr_ref *ref, *_ref;
-	struct jffs2_xattr_ref *xref_tmphash[XREF_TMPHASH_SIZE];
+	struct jffs2_xattr_ref **xref_tmphash;
 	struct jffs2_xattr_datum *xd, *_xd;
 	struct jffs2_inode_cache *ic;
 	struct jffs2_raw_node_ref *raw;
@@ -784,9 +784,12 @@ void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
 
 	BUG_ON(!(c->flags & JFFS2_SB_FLAG_BUILDING));
 
+	xref_tmphash = kcalloc(XREF_TMPHASH_SIZE,
+			       sizeof(struct jffs2_xattr_ref *), GFP_KERNEL);
+	if (!xref_tmphash)
+		return -ENOMEM;
+
 	/* Phase.1 : Merge same xref */
-	for (i=0; i < XREF_TMPHASH_SIZE; i++)
-		xref_tmphash[i] = NULL;
 	for (ref=c->xref_temp; ref; ref=_ref) {
 		struct jffs2_xattr_ref *tmp;
 
@@ -884,6 +887,8 @@ void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c)
 		     "%u of xref (%u dead, %u orphan) found.\n",
 		     xdatum_count, xdatum_unchecked_count, xdatum_orphan_count,
 		     xref_count, xref_dead_count, xref_orphan_count);
+	kfree(xref_tmphash);
+	return 0;
 }
 
 struct jffs2_xattr_datum *jffs2_setup_xattr_datum(struct jffs2_sb_info *c,

fs/jffs2/xattr.h

@@ -71,7 +71,7 @@ static inline int is_xattr_ref_dead(struct jffs2_xattr_ref *ref)
 #ifdef CONFIG_JFFS2_FS_XATTR
 
 extern void jffs2_init_xattr_subsystem(struct jffs2_sb_info *c);
-extern void jffs2_build_xattr_subsystem(struct jffs2_sb_info *c);
+extern int jffs2_build_xattr_subsystem(struct jffs2_sb_info *c);
 extern void jffs2_clear_xattr_subsystem(struct jffs2_sb_info *c);
 
 extern struct jffs2_xattr_datum *jffs2_setup_xattr_datum(struct jffs2_sb_info *c,
@@ -103,7 +103,7 @@ extern ssize_t jffs2_listxattr(struct dentry *, char *, size_t);
 #else
 
 #define jffs2_init_xattr_subsystem(c)
-#define jffs2_build_xattr_subsystem(c)
+#define jffs2_build_xattr_subsystem(c)		(0)
 #define jffs2_clear_xattr_subsystem(c)
 
 #define jffs2_xattr_do_crccheck_inode(c, ic)